The present invention relates generally to the field of fabrication of components. Mechanical components are fabricated in many fashions, including casting and machining. Recently, several techniques have been developed that allow the rapid fabrication of prototypes having a relatively complex geometry. Rapid prototyping techniques are summarized generally in U.S. Pat. No. 5,204,055, issued Apr. 20, 1993, in the name of Sachs et al., entitled Three-Dimensional Printing Techniques (which is incorporated fully herein by reference).
One rapid prototyping technique is known as three-dimensional ("3-D") printing, and is the subject of the '055 Sachs et al. patent application. In 3-D printing, a component is made by depositing a first layer of a porous material in a confined region and then depositing a binder material to selected regions of the layer of porous material to produce a layer of bonded powder material at the selected regions. These steps are repeated a selected number of times to produce successive layers of selected regions of bonded porous material, to form the desired component. The unbonded porous material is then removed. In some cases the component may be further processed as, for example, by heating it to further strengthen the bonding thereof.
The process may be used with a wide variety of powder materials and a wide variety of binders. Ceramic, metallic and polymeric powders may be used. Binders can be comprised of pure solvents or can carry solid material in the form of fine particles, in the form of dissolved matter, or in molten form.
For example, ceramic powder of 30 micron particle size can be spread and a binder comprised of colloidal silica with 0.1 micron silica particles can be printed into the powder. After evaporation of the water in the colloidal silica, the powder bed can be fired and the silica will sinter, resulting in a glass-bonded refractory which is useful as a mold for metal casting or as a filtration medium. The loose powder is removed after the firing operation.
In another embodiment, metal powder, such as stainless steel powder of 60 micron diameter may be spread and then joined by printing a polymeric binder. Suitable polymeric binders include aqueous based materials such as acrylic latex or solvent based systems with dissolved polymers. Printing the polymeric binder defines the green part within the powder bed. The green part can then be removed from the powder bed and post-processed, for example by sintering or by infiltrating in the manner described in U.S. patent application Ser. No. 08/551,012, filed on Oct. 31, 1995, entitled Tooling Made By Three Dimensional Printing, in the names of Samuel Allen et al. Many variations exist regarding this method, and these variations are described in the above referenced Sachs et al. patent, as well as: U.S. Pat. No. 5,387,380, issued on Feb. 7, 1995, in the name of Cima et al., also entitled Three-Dimensional Printing Techniques; U.S. patent application Ser. No. 08/422,384, filed on Apr. 14, 1995, also entitled Three-Dimensional Printing Techniques, in the names of Sachs et al.; and U.S. patent application Ser. No. 08/581,319, filed on Dec. 29, 1995, in the name of James Bredt, entitled Binder Composition for Use in Three Dimensional Printing, all five of which are incorporated fully herein by reference.
The porous material may be loose powder, or, in the alternative, bodies, such as sheets, of lightly bonded powder. If sheets of lightly bonded powder are used, the binding step may use a binder of composition different from that used to lightly bind the power in the sheet. In this manner, after the binding material is applied, the lightly bound powder in the ground regions may be removed by dissolving the binder holding it together in a solvent that does not dissolve the binder applied by printing.
3D printing is conventionally practiced using ink jet printing technology to deliver the liquid binder to the porous material. This has the advantage that the geometry of the printed layer can be changed simply by changing the instructions to the print head. Rather complex geometries can be formed, as they are made one cross-section layer at a time. Further, such technology can be scaled up somewhat by creating a print head with a linear array of nozzles.
It would be desirable to use the basic porous material and binder technology of 3D printing to fabricate very large quantities of parts that have a complex cross-section that is advantageously made using the technology. For instance, it would be desirable to fabricate large quantities of hollow parts for many applications. This would reduce the weight of the parts, and significantly increase the efficiency of any machines in which they were to be incorporated. The parts may have a contoured, varying cross-section that is difficult to fabricate in a hollow configuration using conventional technology, but which could be produced rather easily using 3-D printing. Such parts could be supplied in quantities of millions. In addition to hollow parts, it is desirable to be able to make other parts in large quantities, whose configuration renders normal powder or metallurgy methods unfeasible.
However, 3-D printing has some limitations for the fabrication of such parts in high volume. First, even a large linear array of nozzles must be swept across the full width of the powder bed thus limiting the speed with which an individual layer can be imaged. Second, ink jet printing technology is fairly expensive to build and operate and this may limit the economic capabilities of high volume production with 3-D printing. Further, ink jet printers are relatively delicate and must be carefully adjusted and monitored. The same limitations would also impact the feasibility of making large parts by 3-D printing. The common limitation is a large expanse of powder to be bonded during a relatively short time.
Thus, there is a need for an apparatus and a method that can use the basic technology of 3-D printing: namely a bondable porous material that is bound by a binder, under the high volume, high speed, robust requirements of a full scale industrial operation. There is also a need to minimize the cost of such technology, and to insure its reliability.
Thus, it is an object of the invention to fabricate components on an industrial scale, of both physical dimensions and quantities, using porous material and binder technology, at economical rates and under economical conditions. It is a further object of the invention to produce components having a complex cross-section at a high speed and low cost per component.